Patent GB-1212154-A (GB)
Title: Facsimile transmitter
IPC: H04N1/00
Filed: 1969-04-15
Abstract: 1,212,154. Facsimile transmitter. DIXON AUTOMATIC TOOL Inc. 15 April, 1969 [3 May, 1968], No. 19220/69. Heading H4F. In a facsimile transmitter a document is continuously fed past a scanning position at which a light beam is directed along a path parallel to the surface of, and transversely to the direction of motion of the document, a pair of scanning heads being provided each of which is arranged so that when it is positioned in the light path it directs the beam on to the document and picks up the reflected light and directs it along the path away from the light source, the scanning heads being inserted alternately in the light path to scan the document in one direction and to return along a path offset from the light path. In the basic scanning system, Fig. 32, a light source, comprising a lamp 147, a reflector 163 and lenses 164 and 166, produces a collimated light beam 149 directed across the document 43. A scanner 150 directs and focuses the beam to a point 153 on the document and also receives the reflected light and directs and collimates it into a beam 155 lying in the same straight line as beam 149. Beam 155 is then directed by lens 180 and mirrors 183, 186, 187 on to a photomultiplier 156. Only the scanner 150 is moved and as it crosses the document 43 the illuminated spot scans across with no change in illumination or spot size, this being due to the use of collimated light beams. Two scanners are provided arranged to reciprocate in opposite directions and being arranged so that after one has scanned across the document it is moved out of the light path and returns to its starting position while the second scanner is inserted into the light path and scans the next line in the same direction as the first. As shown, Fig. 14, the two scanners 150, 200 are mounted on carriages 216, 217 sliding on tracks 220, 223 provided in a head 44. Each scanner is mounted on a pivoted arm 226 and is linked to a rocker arm 233 provided with two driving pins 229, 230 which co-operate with oppositely handed helical channels (203, 204) in a pair of driving shafts 201, 202 which are rotated in the same direction. When a scanner is positioned in the light path (as shown for scanner 200) its lower driving pin 230 engages the channel in the lower driving shaft 202 while its upper driving pin 229 is disengaged and when a scanner is positioned on its return path offset from the light path (as shown for scanner 150) its upper drive pin 229 engages the channel of the upper driving shaft and its lower driving pin is disengaged. The scanners are thus arranged so that they move in opposite directions with one in the light path and one in its return path. The helical channels in the driving shafts terminate in cam sections (235, 236) so that as each scanner approaches the end the engaged driving pin is pushed outwards causing the other pin to enter the channel in its associated driving shaft to reverse the direction of motion of the carriage and to simultaneously swing the scanner into or out of the light path as appropriate. The head 44 is supported over the base 45 by a parallelogram linkage (109, 110, 111) and a torsion bar (120) is provided to counterbalance the weight of the head. The document (43) is inserted from the right-hand side of the apparatus in the view of Fig. 14 with the copy side upwards and is continuously driven over an anvil 55 by means of motor-driven rollers 49, 50 against which it is held by pressure rollers 94, 95 mounted on the head 44. A hold-down plate 100 having a slot 101 for the scanning light beam and a yieldable plastics strip 103 to hold the document against the anvil is also mounted on the head 44. The head 44 may be raised and lowered by means of a hand crank (133) via a presettable overload clutch (145) so that the desired pressure may be applied between pressure rollers 94, 95 and the document. This arrangement ensures that the scanner is positioned the same distance from the surface of the document irrespective of its thickness so that the scanning spot is always accurately focused. The driving motor (127) is mounted in the head 44 and is coupled to the rollers 49, 50 by a jointed shaft (66). A hand wheel (83) is incorporated by means of which the rollers 49, 50 can be rotated via a one-way clutch (84) so that the document may be inserted by hand. A switch operating member (91) is provided on the anvil 55 so that the drive motor can be switched on when the document has been inserted. A shutter (255) is provided to occult the light beam during the scanner change over so that a high-intensity beam is not applied directly to the photomultiplier. The anvil 55 is provided with a white strip below the scanning slot 101 in the hold-down plate 100 to improve the contrast obtained with translucent documents. A bundle (189) of optical fibres are connected between the lamp housing and the photomultiplier and circuitry is provided to correct the output for variations in lamp intensity. Synchronizing pulses are generated by a photoelectric element (215) illuminated via an aperture (214) in a drum (213) coupled to the drive motor. The pressure rollers 94, 95 are provided with spaced grooves into which are fitted bands 105 each having a plurality of radially extending deformable fingers (104) which take up any unevenness in the document so that it is transported without skewing. It is stated that two documents differing in thickness by up to 0À01 inch may be fed through the rollers at the same time without either document slipping or skewing.